Generally, the power delivered by an internal-combustion engine depends on the amount of air fed into the combustion chamber, this amount of air being itself proportional to the density of this air.
As it is well known, if high power is required, an increase in this amount of air is provided by compression of the air before it is fed into this combustion chamber. This operation, referred to as supercharging, can be carried out using any means such as a turbocompressor or a driven compressor such as a screw compressor.
Furthermore, in order to increase even further this amount of air in the cylinder, the residual burnt gas initially contained in the dead volume of the combustion chamber is discharged before the end of the engine exhaust phase and it is replaced by supercharged air. This stage is commonly referred to as burnt gas scavenging.
As described in document FR-A-2,886,342, this scavenging can consist in carrying out, at the end of the engine exhaust phase and at the start of the intake phase, overlapping of the exhaust and intake valves of a cylinder. This overlap is obtained by opening simultaneously these exhaust and intake valves for some degrees to some ten degrees of crank rotation angle.
The intake air is thus fed into the combustion chamber before the end of the exhaust phase by expelling the exhaust gas contained therein. This gas is thus discharged through the exhaust valve and replaced by intake air.
Although this type of engine gives satisfaction, it however involves drawbacks that are by no means insignificant.
In fact, such scavenging requires recesses of great depth in the piston, which consequently degrades the shape of the combustion chamber and the progress of the fuel mixture combustion. Furthermore, this type of engine concurrently requires modifying the opening angles of the exhaust valves and the closing angles of the intake valves.
The present invention aims to overcome the aforementioned drawbacks by means of a scavenging method of simple design allowing to improve the limit fuel/air ratio of the fuel mixture and to increase supercharging and filling of the combustion chamber without degrading the shape thereof. Furthermore, particle emissions are limited and the engine power is increased.